The production of gels from water-soluble silicates and acid gelling agents is well known in the art. See Merrill, R. C. et al, The Journal of Physical and Colloidal Chemistry, Vol. 54, p. 806-812 (June 1954); Wills, J. H., "Synthetic Inorganic Silicates", Encyclopedia of Chemical Technology, Vol. 18, 2nd Ed. (1969), John Wiley and Sons, Inc.; and Vail, J. G., "Soluble Silicates, Their Properties and Uses", Vol. 1: Chemistry, Rheinhold Publishing Corp.
The formation of gels from water-soluble polymers is equally well known. U.S. Pat. No. 2,842,338 to Davis et al mixes monomeric calcium acrylate with soil and polymerizes the monomer by cross-linking the acrylic acid groups with the calcium ions to consolidate the soil. U.S. Pat. No. 3,056,757 to Rakowitz gels an acrylamide and methylene-bis-acrylamide mixture using water-soluble salts, such as calcium, aluminum and chromium chlorides, as gelling agents. U.S. Pat. No. 3,421,584 to Eilers et al gels an aqueous system containing water-soluble polymer particles and sodium silicate at a low pH using a gelling agent as a hydrogen ion source. U.S. Pat. No. 3,247,900 to Perry et al polymerizes a monomer in the presence of silica and fluoride ions. U.S. Pat. No. 3,354,084 to Katzer produces a gel from a system containing water, polyacrylamide and silica gel in a finely divided solid form. U.S. Pat. No. 3,749,172 to Hessert et al prepares an aqueous gel from a mixture containing brine, polyacrylamide and amorphous silica.
U.S. Pat. No. 4,031,958 to Sandiford et al extends the above-cited art by combining a partially hydrolyzed polyacrylamide with a gelling agent and sequentially injecting the mixture into a subterranean formation. The polyacrylamide slug is followed by the injection of an alkali metal silicate slug, which contacts the polyacrylamide to form an in situ gel.
The above-cited references describe a number of processes for producing polymer and/or silicate gels. However, the success of these processes for subterranean applications is unpredictable because it is difficult to adequately control the in situ gelation reaction. Gelation reactions are very sensitive to the particular properties and concentrations of the gel components and require good mixing in a favorable environment. If the reaction cannot be controlled at optimum values of these parameters, no gel or, at best, a weak gel is produced and the process fails its intended function for lack of a stable gel.
The problem not solved in the prior art is that of identifying the reaction parameters to which the gelation reaction is most sensitive and controlling these parameters. A process is needed to produce a gel sufficiently stable for subterranean applications such as improved oil recovery or soil consolidation. A process is needed whereby the gel components are uniformly mixed and applied to a porous earthen matrix, such as a subterranean hydrocarbon-bearing formation or unconsolidated soil to produce a homogeneous gel in situ.